Image forming apparatus with sheet transport speed controls to reduce noise

ABSTRACT

An image forming apparatus which can suppress the occurrence of noises without reducing productivity. Sheet transporting units are provided in a paper supply transport section for transporting a sheet to an image forming section, and in a paper ejection transport section for transporting the sheet, on which an image has been formed in the image forming section, to a paper ejection section. When an image is formed on a predetermined sheet, a speed control unit controls a sheet transport speed of at least one of the sheet transporting units provided in the paper supply transport section and the paper ejection transport section to be higher than that in the image forming section.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an image forming apparatus, andmore particularly to an apparatus which controls the transport speed ofa sheet.

[0003] 2. Description of the Related Art

[0004]FIG. 7 shows the construction of a conventional image formingapparatus. Referring to FIG. 7, numeral 1 denotes an image formingsection for forming an image through an electrophotographic process. Theimage forming section 1 comprises a photoconductive drum 10, a laserscanner 9 for illuminating light to the surface of the photoconductivedrum 10 to form an electrostatic latent image on it, and a developingstation 11 for developing the latent image formed on the photoconductivedrum 10.

[0005] Also, numeral 2 denotes a cassette for accommodating sheets ofrecording paper 3, and numeral 6 denotes a paper supply transportsection for feeding the sheets of recording paper 3 to the image formingsection 1 one by one. The paper supply transport section 6 comprises areversing guide 7 for introducing the recording paper 3 to the imageforming section 1 in a reversed state, register rollers 8 for correctinga skew of the recording paper 3. Numeral 14 denotes a paper ejectiontransport section for transporting the recording paper 3, on which animage has been formed in the image forming section 1, to a paperejection tray 17 that serves as a paper ejecting section. The paperejection transport section 14 comprises a reversing guide 15 and a paperejection roller 16 for introducing the recording paper 3 to the paperejection tray 17.

[0006] When an image is formed in the image forming apparatus thusconstructed, one of the sheets of recording paper 3 accommodated in thecassette 2 is first picked up by a pickup roller 4 and then separated bya separator 5 for feeding to the paper supply transport section 6. Then,the recording paper 3 passes the reversing guide 7 and is introduced tothe image forming section 1 after a skew of the recording paper 3 hasbeen corrected by the register rollers 8.

[0007] Subsequently, when the recording paper 3 passes a top sensor 18disposed immediately upstream of the image forming section 1, the laserscanner 9 for the image forming section 1 starts operation insynchronization. The laser scanner 9 irradiates a laser beam onto thephotoconductive drum 10 to form an electrostatic latent image thereon.Then, the electrostatic latent image is developed into a visible imageand transferred to the recording paper 3 in a transferring station 12.

[0008] After the transfer of the visible image, the recording paper 3 isguided to a fusing station 13 by a guide 19. The visible image is fusedand fixed in the fusing station 13 under heating and pressure, wherebythe image formation is completed. Then, the recording paper 3 isadvanced to the paper ejection transport section 14 and ejected onto thepaper ejection tray 17 by the paper ejection roller 16 after passing thereversing guide 15.

[0009] In such a conventional image forming apparatus, efforts have beenmade to transport the recording paper 3 at a sheet transport speed inthe paper supply transport section 6 and the paper ejection transportsection 14 about twice that in the image forming section 1, i.e., aprocess speed, for the purpose of reducing a fast copying time.

[0010] However, efforts at increasing the sheet transport speed havecaused problems. When outputting 20 copies of the same original documentsuccessively, for example, an increase of the sheet transport speed inthe paper supply transport section 6 and the paper ejection transportsection 14 generates increased noise due to an increase in frictionallysliding sounds between the recording paper 3 and the reversing guides 7,15, to collision sounds generated due to backlashes in engagementbetween gears at the time of start and stop, to collision sounds fromclutches for transmitting torques to transport rollers, to soundsoccurring when the recording paper 3 strikes against the registerrollers 8 when a skew of the recording paper 3 is compensated for, andto sounds occurring when the recording paper 3 strikes against thereversing guide 7 when the recording paper 3 is looped. In particular,when the reversing guides 7, 15 are curved as shown in FIG. 7, thefrictionally sliding sounds between the recording paper 3 and thereversing guides 7, 15 become more noticeable.

[0011] Further, a larger current must be supplied to each motor, etc.,for achieving increased speed. This necessarily increases the amount ofheat generated by the motor and raises motor temperature. Such increaseof motor temperature not only deteriorates reliability of the motoritself, but also raise a temperature in the apparatus body. Thistemperature rise in the apparatus body causes an adverse effect upon theimage forming section.

[0012] A fan or the like may be used to cool the image forming sectionfor suppressing the adverse effect due to such a temperature rise. Thiscase however would increase the costs. In the case of slowing down thesheet transport speed for the same purpose, overall productivity (timerequired for completion of a print) would be reduced.

SUMMARY OF THE INVENTION

[0013] In view of the state of the art set forth above, it is an objectof the present invention to provide an image forming apparatus capableof suppressing noise without reducing productivity.

[0014] To achieve the above object, according to one aspect of thepresent invention, there is provided an image forming apparatuscomprising an image forming section, a paper supply transport sectionfor transporting a sheet to the image forming section, and a paperejection transport section for transporting the sheet, on which an imagehas been formed in the image forming section, to a paper ejectionsection, the apparatus further comprising a sheet transporting unitprovided in each of the paper supply transport section and the paperejection transport section; and a speed control unit for controllingsheet transport speeds of each of the sheet transporting units, thespeed control unit controlling the sheet transport speed of at least oneof the sheet transporting units provided in the paper supply transportsection and the paper ejection transport section to be higher than thesheet transporting speed in the image forming section when an image isformed on a predetermined sheet.

[0015] Also, according to the present invention, an image formingapparatus comprises an image forming section, a paper supply transportsection for transporting a sheet to the image forming section, a sheettransporting unit provided in the paper supply transport section, and aspeed control unit for controlling a sheet transport speed of the sheettransporting unit, the speed control unit controlling the sheettransport speed of the sheet transporting unit provided in the papersupply transport section to be higher than a sheet transporting speed inthe image forming section during image formation.

[0016] Further, according to the present invention, the predeterminedsheet is the last or first one when images are successively formed on aplurality of sheets.

[0017] Still further, according to the present invention, each sheettransporting unit is driven by a stepping motor, and the speed controlunit controls the sheet transport speed of each sheet transporting unitby controlling the respective stepping motor.

[0018] Still further, according to the present invention, the papersupply transport section or the paper ejection transport sectionincludes a curved sheet transport path.

[0019] Still further, according to the present invention, the imageforming apparatus further comprises a re-transport section fortransporting a sheet, on one side of which an image has been formed,back to the image forming section for forming an image on the other sideof the sheet having the image formed on one side thereof; and a sheettransporting unit provided in the re-transport section, the speedcontrol unit controlling the sheet transport speed of the sheettransporting unit provided in at least one of the re-transport section,the paper supply transport section and the paper ejection transportsection to be higher than the sheet transport speed in the image formingsection during image formation on the other side of the last sheet.

[0020] Still further, according to the present invention, a paperejecting unit for ejecting a sheet to the paper ejection section isprovided in the paper ejection transport section, and the speed controlunit controls the paper ejecting unit to eject the sheet at apredetermined sheet ejection speed regardless of the sheet transportspeed in the paper ejection transport section.

[0021] Thus, according to the present invention, the sheet transportingunits are provided in the paper supply transport section fortransporting a sheet to the image forming section, and in the paperejection transport section for transporting the sheet, on which an imagehas been formed in the image forming section, to the paper ejectionsection. When an image is formed on a predetermined sheet, the speedcontrol unit controls the sheet transport speed of at lease one of thesheet transporting units provided in the paper supply transport sectionand the paper ejection transport section to be higher than that in theimage forming section.

[0022] Further objects, features and advantages of the present inventionwill become apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a view schematically showing the construction of acopying machine as one of image forming apparatus according to anembodiment of the present invention;

[0024]FIG. 2 is a control block diagram of the copying machine of FIG.1;

[0025]FIG. 3 shows a condition where a sheet of recording paper isincorrectly ejected in the copying machine of FIG. 1;

[0026]FIGS. 4A and 4B are charts for explaining the sheet transportoperation in the related art and the copying machine of FIG. 1;

[0027]FIG. 5 is a flowchart for explaining transport speed control inthe copying machine of FIG. 1;

[0028]FIG. 6 is a view for explaining the registering operation in apaper supply transport section; and

[0029]FIG. 7 is a view schematically showing the construction of aconventional image forming apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] An embodiment of the present invention will be described below indetail with reference to the drawings.

[0031]FIG. 1 schematically shows the construction of a copying machineas one of image forming apparatus according to an embodiment of thepresent invention. Note that, in FIG. 1, the same numerals as in FIG. 7denote the same or corresponding components.

[0032] Referring to FIG. 1, numeral 100 denotes a copying machine and100A denotes a body of the copying machine. Numeral 22 denotes a readingunit which may serve as reading means for reading an original document(not shown) placed on a platen 21. Document information read by thereading unit 22 is sent to a laser scanner 9. In accordance with thedocument information, the laser scanner 9 illuminates light to thesurface of a photoconductive drum 10 to form thereon an electrostaticlatent image.

[0033] Numerals 6 a, 6 b denote feed rollers disposed in the papersupply transport section 6. A sheet of recording paper 3 is transportedto an image forming section 1 by the feed rollers 6 a, 6 b and registerrollers 8. Also, numeral denotes a manual paper supply section. A sheetof recording paper (not shown) manually inserted through the manualpaper supply section 25 is transported to the image forming section 1 bythe feed rollers 6 a, 6 b and a paper supply roller 26.

[0034] Numerals 14 a, 14 b denote feed rollers disposed in the paperejection transport section 14. The recording paper 3, on which an imagehas been formed in the image forming section 1, is transported by thefeed rollers 14 a, 14 b to a paper ejection roller 16 that serves as apaper ejecting means. Thereafter, the recording paper 3 is ejected bythe paper ejection roller 16 onto a paper ejection tray 17 that isformed in a central area of the copying machine body 100A.

[0035] Further, numeral 20 denotes a fusing sensor disposed downstreamof a fusing station 13. The fusing sensor 20 is turned on upon detectingthe leading end of the recording paper 3 on which a visible image hasbeen fused and fixed in the fusing station 13, and is turned off afterthe tailing end of the recording paper 3 has passed the fusing sensor20. An output of the fusing sensor 20 is applied to a control unit 30,shown in FIG. 2, provided at a predetermined position within the copyingmachine.

[0036] The control unit 30 serving as a speed control means detects thenumber of sheets of recording paper 3, on which images have been formed,in accordance with the output of the fusing sensor 20. Depending on thedetected number of sheets having images recorded thereon, the controlunit 30 controls rotations of a first driving motor M1 (FIG. 2) fordriving the rollers 4, 5, 6 a, 6 b, 8 and 26 that constitute papersupply sheet transporting means of the paper supply transport section 6,a second driving motor M2 for driving the rollers 14 a, 14 b thatconstitute paper ejection sheet transporting means of the paper ejectiontransport section 14, and a third driving motor M3 for driving the paperejection roller 16, thereby controlling the transport speed of therecording paper 3.

[0037] In this embodiment, stepping motors are used as the first tothird driving motors M1, M2 and M3. The control unit 30 changes pulsecommands to control the rotational speeds of the driving motors M1, M2and M3 so that the transport speed of the recording paper 3 iscontrolled as intended. The use of stepping motors, whose speeds can beeasily controlled just by changing pulse commands, eliminates the needof separately adding other mechanisms, such as drive gears and clutches,for changing the sheet transport speed, and is effective to avoid anincrease of the cost.

[0038] When forming images on, e.g., 20 sheets of recording paper 3successively, the control unit 30 rotates the first driving motor M1 andthe second driving motor M2 in this embodiment such that the sheettransport speed in the paper supply transport section 6 and the paperejection transport section 14 is the same as that in the image formingsection 1, i.e., a process speed, until reaching the last sheet ofrecording paper 3.

[0039] Also, at the time when the recording paper 3 is ejected by thepaper ejection roller 16 to such an extent that a sheet rear portion ofabout 10 mm still has not yet passed the paper ejection roller 16, thecontrol unit 30 controls the rotation of the third driving motor M3 torotate the paper ejection roller 16 at a speed (referred to as a “doublespeed” hereinafter) twice the process speed. By rotating the paperejection roller 16 at double speed, the tailing end of recording paper 3is prevented from striking against wall 23 of paper ejection tray 17, asshown in FIG. 3.

[0040] On the other hand, when forming an image on the last sheet ofrecording paper 3, the control unit 30 rotates the first driving motorM1 and the second driving motor M2 after the start of paper supply suchthat the sheet transport speed in at least one of the paper supplytransport section 6 and the paper ejection transport section 14, in bothof them in this embodiment, is the speed twice the process speed for thepurpose of improving productivity.

[0041] Furthermore, at the time when the control unit 30 receives asignal from the a top sensor 18, which indicates the detection of therecording paper 3, after doubling the sheet transport speed in the papersupply transport section 6, it rotates the first driving motor M1 suchthat the recording paper 3 is transported at the process speed for imageformation. Then, when an off-signal is inputted from the fusing sensor20, i.e., when the image formation is completed, the control unit 30rotates the second driving motor M2 so as to double the transport speedof the recording paper 3 in the paper ejection transport section 14.

[0042]FIG. 4B is a chart for explaining the sheet transport operation inthe copying machine 100 having the above-described construction. In thechart of FIG. 4B, the vertical axis represents the distance of movementof the recording paper 3 and the horizontal axis represents time. FIG.4A represents the sheet transport operation in a conventional copyingmachine.

[0043] Comparing the transport operation of the recording paper 3 shownin FIG. 4B with that in the related art shown in FIG. 4A, a time T3required for outputting one copy in this embodiment is longer than atime T1 required in the related art. This difference in copying timeresults from the fact that a characteristic line of the related art hasa steeper gradient in two regions as shown in FIG. 4A, while acharacteristic line of this embodiment has a uniform gradient as shownin FIG. 4B.

[0044] However, a time interval T2 for paper supply is the same betweenthe related art and this embodiment whenever each copying machine hasthe same printing capability. Assuming specifications whereby sheets ofrecording paper are supplied at a rate of 20 sheets/min, for example,the sheets are supplied at the time interval T2 of 60 (seconds)/20(sheets)=3 seconds per sheet in either case. As is understood from FIG.4B, therefore, a total time T4 in this embodiment is the same as that inthe related art by transporting with only the last sheet of recordingpaper 3 at a faster speed, i.e., in the same time as T1 in the relatedart. In the case of forming only one copy, the first sheet of recordingpaper is the last sheet of recording paper 3, and therefore the fastcopying time is not reduced.

[0045] By controlling the sheet transport speed as described above, theneed for transporting the recording paper 3 at an increased speed can beeliminated and the generation of noises can be prevented. Also, sincethe driving motors M1, M2 and M3 are no longer required to rotate at anincreased speed, it is possible to prevent a temperature rise in thecopying machine body due to heat generated by the driving motors M1, M2and M3, and hence to avoid an adverse effect upon the image formingsection 1.

[0046] The transport speed control of the copying machine 100 having theabove-described construction will be described below with reference to aflowchart of FIG. 5. Herein, a description is made of, by way ofexample, the operation in the case of copying images on 20 sheets ofrecording paper 3 successively.

[0047] First, in STEP 1, an operator sets an original document on theplaten 21 shown in FIG. 1, and sets the number of copies to 20 byentering a numeral 20 through a key-in section (not shown) provided in aconsole 31 shown in FIG. 2. Then, the operator depresses a start buttonto start the copying operation.

[0048] In STEP 2, when the start button is depressed, the control unit30 determines whether the recording paper 3 is the last sheet ofrecording paper, i.e., whether it is the 20-th sheet. If it isdetermined that the recording paper 3 is the last sheet of recordingpaper, the control unit 30 controls the rotation of the first drivingmotor M1 so that the sheet transport speed through the pickup roller 4,the separator 5, the register rollers 8, and the feed rollers 6 a, 6 bis the same as the process speed.

[0049] Subsequently, the recording paper 3 is transported at such atransport speed, and when the recording paper 3 is detected by the topsensor 18 disposed immediately upstream of the image forming section 1,the control unit 30 controls the process of image formation in sync withimage information. At this time, the sheet transport speed remains atthe process speed. Thereafter, the fusing sensor 20 is turned on whilethe image formation is continued. If no jam is detected, the controlunit 30 rotates the first driving motor M1 so that the pickup roller 4automatically starts operation at 3 seconds after the start of thepreceding paper supply cycle, thereby supplying a next sheet ofrecording paper. In such a sequence, time management is carried outusing a timer 32 shown in FIG. 2.

[0050] In STEP 3, after completion of the image formation including thefusing process, at the time when the tailing end of the recording paper3 introduced to the paper ejection transport section 14 passes thefusing sensor 20, the fusing sensor 20 is turned off. Upon the fusingsensor being turned off, the control unit 30 controls the rotation ofthe second driving motor M2 so that the sheet transport speed throughthe feed rollers 14 a, 14 b in the paper ejection transport section 14is the same as the process speed.

[0051] Then, at the time when the recording paper 3 having been fedthrough the paper ejection transport section 14 at the process speed isejected onto the paper ejection tray 17 by the paper ejection roller 16to such an extent that a sheet rear portion of about 10 mm has not yetpassed the paper ejection roller 16, the control unit 30 rotates thethird driving motor M3 such that the sheet transport speed becomes twicethe process speed.

[0052] Hence, as described above, the tailing end of the recording paper3 is ejected onto the paper ejection tray 17 without striking againstthe wall 23 of the paper ejection tray 17 as shown in FIG. 3. The timingof increasing the sheet transport speed in such a sequence is alsodetermined under the time management using the timer 32.

[0053] In STEP 4, the above-described copying operation is repeated, andwhen the last 20-th sheet of recording paper 3 is finally reached, thecontrol unit 30 controls the rotation of the first driving motor M1after the start of paper supply so that the sheet transport speed isdoubled until the top sensor 18 detects the recording paper 3, for thepurpose of reducing a time necessary for the job of printing 20 copies,i.e., improving productivity.

[0054] Subsequently, when the recording paper 3 is detected by the topsensor 18, the control unit 30 controls the process of image formationin sync with image information. At this time, the sheet transport speedis reduced to the process speed for the image formation. Then, when thefusing sensor 20 is turned off, i.e., when the image formation iscompleted, the control unit 30 controls the rotation of the seconddriving motor M2 so as to double the sheet transport speed in the paperejection transport section 14.

[0055] Thereafter, the recording paper 3 is ejected onto the paperejection tray by the paper ejection roller 16. In this case, when therecording paper 3 is ejected by the paper ejection roller 16, the sheettransport speed in the paper ejection transport section 14 is alreadydoubled. Therefore, the paper ejection roller 16 ejects the recordingpaper 3 onto the paper ejection tray without changing its rotationalspeed for a rear end portion of the recording paper 3.

[0056] Thus, in the case of outputting copies successively, thecontinuous copying operation can be performed with less noise andwithout reducing productivity by increasing the transport speed of onlythe last sheet of recording paper 3, i.e., by avoiding the unnecessaryincreased transporting speed of sheets of recording paper 3.

[0057] Also, by increasing the sheet transport speed not in the papersupply transport section 6 alone, but in both of the paper supplytransport section 6 and the paper ejection transport section 14, noiseis reduced over an entire paper path and hence a quieting effect isachieved.

[0058] Further, since the driving motors M1, M2 and M3 are not requiredto rotate at the increased speed unnecessarily, heat generation from thedriving motors M1, M2 and M3 can be suppressed. It is therefore possibleto prevent an adverse effect upon the image forming section 1 resultingfrom a temperature rise in the copying machine body, and an increase ofthe cost resulting from the necessity of a cooling fan, etc.

[0059] Moreover, as shown in FIG. 1, the transport path in the papersupply transport section 6 is generally introduced to the registerrollers 8 while passing the curved reversing guide 15 immediately afterexiting the cassette 2.

[0060] The register rollers 8 are essential to correct a skew of therecording paper 3 before it enters the image forming section 1, and toadjust the image write timing.

[0061] Although the register rollers 8 are essential in the transportpath in the paper supply transport section 6, the recording paper 3strikes against the register rollers 8 at a standstill, as shown in FIG.6, when the recording paper 3 is registered. From the viewpoint ofoperating noises, therefore, a higher transport speed in the papersupply transport section 6 increases the sound generated upon bucklingof the recording paper 3 itself, the sound generated upon the recordingpaper 3 striking against the inverting guide 7 after being buckled, andthe sound generated upon the recording paper 3 frictionally sliding overthe reversing guide 7 when the recording paper 3 moves again afterforming a loop while it is pressed against the surface of the reversingguide 7 under resiliency of the loop.

[0062] Additionally, in most cases, the paper supply transport section 6includes the manual paper supply section 25 for manual paper supplymidway in the transport path, as shown in FIG. 1. In this arrangement,sounds such as one generated upon the sheet registration are apt to leakto the outside through a paper supply opening 28.

[0063] Stated otherwise, the paper supply transport section 6 has anarrangement including many noise sources such as the register rollers,and causing sounds to easily leak through the opening for the manualpaper supply section. Therefore, increasing the transport speed of onlythe last sheet of recording paper 3 in the paper supply transportsection 6, as one feature of the present invention, is very effective tosuppress such noise.

[0064] More specifically, the copying machine 100 of this embodimentincludes the curved reversing guides 7, 15 as shown in FIG. 1. When therecording paper 3 passes the curved reversing guides 7, 15, sounds aregenerated due to frictionally sliding of the recording paper 3 over thecurved reversing guides 7, 15 and are increased especially in the caseof using the recording paper 3 that has strong rigidity or is recycledpaper having a rough surface.

[0065] However, even those noises can be reduced by increasing thetransport speed of only the last sheet of recording paper 3.

[0066] While only the last sheet of recording paper 3 is sped up in thedescription set forth above, the present invention is not limited tosuch an embodiment and the first sheet of recording paper 3, forexample, may be sped up instead of the last sheet of recording paper 3.

[0067] Speeding up the first sheet of recording paper 3 is advantageousin enabling errors, such as a copying error and other errors in densitycontrast and size, to be earlier found. By depressing a stop key at onceupon confirmation of such an error, the number of wasted sheets ofrecording paper 3 can be minimized.

[0068] Further, as shown in FIG. 1, the copying machine 100 of thisembodiment includes a re-transport section 27 for transporting therecording paper 3 back to the image forming section 1 to form an imageon the other side of the recording paper 3, on one side of which animage has been already formed, for the purpose of duplex recording.

[0069] When performing duplex recording, the recording paper 3, on oneside of which an image has been already formed, is first transported tothe paper ejection transport section 14. Then, the feed roller 14 a isrotated backward to advance the recording paper 3 into the re-transportsection 27. Subsequently, the recording paper 3 is sent back to thepaper supply transport section 6 by feed rollers 27 a, 27 d, which serveas re-transport sheet transporting means and is disposed in there-transport section 27, and then transported to the image formingsection 1.

[0070] In such a process of forming images on both sides of therecording paper 3, at least one of the sheet transport speeds in thepaper supply transport section 6, the paper ejection transport section14, and the re-transport section 27, e.g., all of those sheet transportspeeds in this embodiment, is increased to twice the process speed butonly when an image is formed on the other surface of the last sheet ofthe recording paper 3. As a result, a reduction of noises can berealized.

[0071] While the copying machine 100 includes one stage of cassette 2 inthe foregoing embodiment, the present invention is not limited to suchan arrangement, and similar advantages can also be obtained by makingsimilar control in a copying machine provided with a plurality ofcassettes. Stated otherwise, in a copying machine including a pluralityof cassettes 2, similar advantages can be obtained by controlling thetransport speed of the recording paper 3 until reaching the imageforming section 1 from a paper supply opening of each of the cassettes.This is equally applied to the transport of the recording paper 3 fromthe manual paper supply section 25. It is thus essential that the sheettransport speed in the paper supply transport section 6 from each papersupply section to the image forming section 1 be controlled.

[0072] Further, while the transport speed is increased for the lastsheet of recording paper 3 or the first sheet of recording paper 3 inthe foregoing description, the transport speeds may be increased forboth of the last sheet and the first sheet, and the sheet of recordingpaper 3, which should be sped up, may be set depending on the preferenceof users. Also, frequency of the speed control may be changed dependingon the type of recording paper 3. Thus, in the case of using thick paperor recycled paper that is apt to cause noises, only the last sheet ofrecording paper 3 may be transported at the double speed. Further, theimage forming section 1 may be of the type of, e.g., bubble jet, thermaltransfer, and dot impact. It is just essential that the image formingsection 1 is able to record an image on a sheet of recording papertransported through it.

[0073] The embodiment has been described as speeding up the recordingpaper for its rear end portion of 10 mm when the recording paper isejected at the process speed. However, the transport speed may beoptionally adjusted to a proper value for the rear end portion of therecording paper depending on alignment of sheets ejected in the stackedform.

[0074] More specifically, for example, when the recording paper 3 isoverly ejected in the speed-up ejection mode, or when the paper ejectiontray 17 has a specific shape, the recording paper 3 may be ejected atthe same speed when it is transported at the process speed, and thetransport speed of the recording paper 3 may be reduced for the rear endportion of 10 mm when ejected at the double speed. By thus controllingthe paper ejection by the paper ejection roller 16 so as to eject thesheet of recording paper 3 at a predetermined ejection speed regardlessof the paper ejection transport section 14, it is possible to improvealignment of the stacked sheets of recording paper 3 and operability intaking out and putting the sheets in order.

[0075] According to the present invention, as has been described above,the occurrence of noises can be suppressed without reducing productivityby controlling the sheet transport speed of at least one of sheettransporting means provided in the paper supply transport section andthe paper ejection transport section to be higher than that in the imageforming section when an image is formed on a predetermined sheet.

[0076] While the present invention has been described with reference towhat are presently considered to be the preferred embodiments, it is tobe understood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. An image forming apparatus comprising an imageforming section, a sheet supply transport section for transporting asheet to the image forming section, and a sheet ejection transportsection for transporting the sheet, on which an image has been formed insaid image forming section, said apparatus further comprising: sheetsupply transporting means for transporting sheets in said sheet supplytransport section; sheet ejection transporting means for transportingsheets in said sheet ejection transport section; and speed control meansfor controlling sheet transport speeds of said sheet supply transportingmeans and said sheet ejection transporting means, said speed controlmeans controlling the sheet transport speed of at least one of saidsheet supply transporting means and said paper ejection transportingmeans to be higher than a sheet transporting speed in the image formingsection during transportation of a predetermined sheet.
 2. An imageforming apparatus comprising: an image forming section; a sheet supplytransport section for transporting a sheet to said image formingsection; sheet supply transporting means for transporting sheets in saidsheet supply transport section; and speed control means for controllinga sheet transport speed of said sheet supply transporting means, saidspeed control means controlling the sheet transport speed of said sheetsupply transporting means to be higher than a sheet transporting speedin said image forming section during transportation of a predeterminedsheet.
 3. An image forming apparatus according to claim 1, wherein saidspeed control means sets the higher transport speed on at least one of alast and first sheet of sequential sheets on which images are formed. 4.An image forming apparatus according to claim 1, wherein each of saidsheet supply transporting means and said sheet ejection transportingmeans is driven by a stepping motor, and said speed control meanscontrols the sheet transport speed of said sheet supply transportingmeans and said sheet ejection transporting means by controlling saidstepping motors.
 5. An image forming apparatus according to claim 1,wherein at least one of said sheet supply transport section and saidsheet ejection transport section includes a curved sheet transport path.6. An image forming apparatus according to claim 1, further comprising:a re-transport section for transporting a sheet, on one side of which animage has been formed, back to said image forming section for forming animage on the other side of said sheet having the image formed on oneside thereof; and re-transport sheet transporting means for transportingthe sheet in said re-transport section back to the image formingsection, said speed control means controlling the sheet transport speedof at least one of said re-transport sheet transporting means, saidsheet supply transporting means and said sheet ejection transportingmeans to be higher than a sheet transporting speed in said image formingsection during transportation of a predetermined sheet for imageformation on the other side of said predetermined sheet.
 7. An imageforming apparatus according to claim 1, wherein sheet ejecting means forejecting a sheet from said sheet ejection transport section is providedin said paper ejection transport section, and said speed control meanscontrols said sheet ejecting means to eject the sheet at a predeterminedsheet ejection speed regardless of a sheet transport speed of said sheetejection transporting means.